-20.1 Shell Script Introduction -20.2 Shell script structure and execution -20.3 date command usage -20.4 variables in shell scripts # 20.1 Shell script introduction -Shell is a scripting language Follow aming_linux blog.lishiming.net -Can use syntax such as logical judgment, loop, etc. -Can customize functions -shell is a collection of system commands -Shell script can realize automatic operation and maintenance, which can greatly increase our operation and maintenance efficiency # 20.2 Shell script structure and execution -You need to add #! / Bin / bahs at the beginning // Tell the system which interpreter this script uses to operate -Lines beginning with # as explanation -The name of the script ends with .sh to distinguish this is a shell script -Create a shell directory first `` ` [[email protected] ~] # clear [[email protected] ~] # mkdir shell [[email protected] ~] # cd shell / [[email protected] shell] # ls [[email protected] shell] # vi 01.sh #! / bin / bash echo "123" w ls ~ ~ : wq [[email protected] shell] # vi 01.sh `` ` -There are two implementation methods: chmod + x 1.sh; ./1.sh bash 1.sh, sh 1.sh `` ` [[email protected] shell] # sh 01.sh 123 21:07:19 up 5 min, 2 users, load average: 0.04, 0.33, 0.20 USER TTY FROM [email protected] IDLE JCPU PCPU WHAT root tty1 21:02 4:39 0.02s 0.02s -bash root pts / 0 192.168.202.1 21:03 7.00s 0.03s 0.01s w 01.sh [[email protected] shell] # `` ` -Another way, the beginning of the file means that the next command is parsed by this file. `` ` [[email protected] shell] # chmod a + x 01.sh [[email protected] shell] # ./01.sh 123 21:09:48 up 7 min, 2 users, load average: 0.14, 0.23, 0.18 USER TTY FROM [email protected] IDLE JCPU PCPU WHAT root tty1 21:02 7:08 0.02s 0.02s -bash root pts / 0 192.168.202.1 21:03 4.00s 0.03s 0.00s / bin / bash ./01.sh 01.sh [[email protected] shell] # [[email protected] shell] # cat 01.sh #! / bin / bash echo "123" w ls [[email protected] shell] # `` ` -bin / bash is actually bin / sh `` ` [[email protected] shell] # ls -l / bin / bash -rwxr-xr-x. 1 root root 960392 August 3 2016 / bin / bash [[email protected] shell] # ls -l / bin / sh lrwxrwxrwx. 1 root root 4 October 5 22:18 / bin / sh-> bash [[email protected] shell] # `` ` -View the script execution process, each + represents a step `` ` [[email protected] shell] # sh -x 01.sh + echo 123 123 + w 21:17:01 up 14 min, 2 users, load average: 0.02, 0.07, 0.12 USER TTY FROM [email protected] IDLE JCPU PCPU WHAT root tty1 21:02 14:21 0.02s 0.02s -bash root pts / 0 192.168.202.1 21:03 5.00s 0.05s 0.00s sh -x 01.sh + ls 01.sh [[email protected] shell] # `` ` -You can also use sh -n to see if the syntax of the script is correct -No output, indicating no errors `` ` [[email protected] shell] # sh -n 01.sh [[email protected] shell] # `` ` -Modify the file to test the error `` ` [[email protected] shell] # sh -n 01.sh [[email protected] shell] # vi 01.sh #! / bin / bash echo "123" w ls for i in `seq 1 10` do echo $ i ~ ~ ~ : wq `` ` -Run sh -n again `` ` [[email protected] shell] # sh -n 01.sh 01.sh: line 8: syntax error: unexpected end of file [[email protected] shell] # `` ` -Change back `` ` [[email protected] shell] # vi 01.sh #! / bin / bash echo "123" w ls ~ ~ ~ : wq `` ` -Monitoring is useless `` ` [[email protected] shell] # sh -n 01.sh [[email protected] shell] # `` ` # 20.3 date command usage -date is very useful in shell; add a time to file suffix for later management -date +% Y-% m-% d, date +% y-% m-d `` ` [[email protected] ~] # date Monday, November 20, 2017 22:01:01 CST [[email protected] ~] # `` ` -m months, M minutes `` ` [[email protected] ~] # date Monday, November 20, 2017 22:01:01 CST [[email protected] ~] # date +% Y 2017 [[email protected] ~] # date +% y 17 [[email protected] ~] # date +% m 11 [[email protected] ~] # date +% M 27 [[email protected] ~] # `` ` -Date d Big D `` ` [[email protected] ~] # date +% d 20 [[email protected] ~] # date +% D 11/20/17 [[email protected] ~] # `` ` -Date, year, month, day date +% Y% m% d `` ` [[email protected] ~] # date +% Y% m% d 20171120 [[email protected] ~] # `` ` -Date +% F `` ` [[email protected] ~] # date +% F 2017-11-20 [[email protected] ~] # `` ` -Hours, minutes, seconds -s represents a timestamp indicating how many seconds have elapsed since January 1, 1970, 0: 0 `` ` [[email protected] ~] # date +% H twenty two [[email protected] ~] # date +% s 1511188397 [[email protected] ~] # date +% S twenty two [[email protected] ~] # date +% S 32 [[email protected] ~] # `` ` -About time -date +% T -date +% H% M% S `` ` [[email protected] ~] # date +% T 22:35:38 [[email protected] ~] # date +% H% M% S 223608 [[email protected] ~] # `` ` -h shows the month, `` ` [[email protected] ~] # date +% h November [[email protected] ~] # `` ` -Change language to English first `` ` [[email protected] ~] # LANG = en [[email protected] ~] # date +% h Nov [[email protected] ~] # `` ` -Add a colon date +% H:% M:% S is equivalent to date +% T `` ` [[email protected] ~] # date +% H:% M:% S 22:42:38 [[email protected] ~] # date +% T 22:42:42 [[email protected] ~] # `` ` -Week -w day -W weeks of the year `` ` [[email protected] ~] # date +% w 1 [[email protected] ~] # date +% W 47 [[email protected] ~] # `` ` -Show calendar cal `` ` [[email protected] ~] # cal November 2017 Su Mo Tu We Th Fr Sa 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 [[email protected] ~] # `` ` -date -d "+1 day" +% F one day later -date -d "-1 day" +% F a day ago -date -d "-1 month" +% F a month ago -date -d "-1 min" +% F one minute ago -date -d "-1 year" +% F one year ago -Mark yesterday's date date -d "-1 day" `` ` [[email protected] ~] # date Mon Nov 20 23:07:38 CST 2017 [[email protected] ~] # date -d "-1 day" Sun Nov 19 23:07:46 CST 2017 [[email protected] ~] # [[email protected] ~] # date -d "-1 day" +% F 2017-11-19 [[email protected] ~] # `` ` -Last month date -d "-1 month" `` ` [[email protected] ~] # date -d "-1 month" +% F 2017-10-20 [[email protected] ~] # `` ` -Last year date -d "-1 year" `` ` [[email protected] ~] # date -d "-1 year" +% F 2016-11-20 [[email protected] ~] # date -d "-1 year" Sun Nov 20 23:10:43 CST 2016 [[email protected] ~] # `` ` -Last hour date -d "-1 hour" `` ` [[email protected] ~] # date -d "-1 hour" +% T 22:11:43 [[email protected] ~] # `` ` -Timestamp is converted to specific date and time `` ` [[email protected] ~] # date +% s 1511190759 [[email protected] ~] # [[email protected] ~] # date -d @ 1511190759 Mon Nov 20 23:12:39 CST 2017 [[email protected] ~] # [[email protected] ~] # date +% s -d "2017-11-20 23:12:39" 1511190759 [[email protected] ~] # `` ` # 20.4 variables in shell scripts -Variables should be used when a certain string is used frequently in a script -When using conditional statements, often use the variable if [$ a -gt 1]; then ...; fi -When referring to the result of a command, replace n = `wc -l 1.txt` with a variable -Variables are also essential when writing scripts that interact with users. Read -p "Input a number:" n; echo $ n If you don't write this n, you can use $ REPLY directly -Built-in variables $ 0, $ 1, $ 2 ... $ 0 represents the script itself, $ 1 is the first parameter, $ 2 is the second .... $ # is the number of parameters -Math operations a = 1; b = 2; c = $ (($ a + $ b)) or $ [$ a + $ b]
20.1 shell script introduces 20.2 shell script structure and executes 20.3 date command usage 20.4 A variable in a shell script
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